Process for esterifying acyloxy carboxylic acids



Patented June 18, 1946 UNITED STATE.

PROCESS FOR ESTERIFYING ACYLOXY CARBOXYLIC ACIDS Edward M. Filachione,Philadelphia, Pa., assignor to the United No Drawing.

States of America as rep- 7 resented by the Secretary of AgricultureApplication December 27, 1943, Serial No. 515,800

1 Claim. (01. 260-484) (Granted under the act of March 3, 1883, as

1 amended April 30, 1928; 3'70 0. G. 757) This application is made underMarch 3, 1883, as amended by the act of April 30, 1928, and theinvention herein described, it patented, may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment to me of any royalty thereon.

This invention relates to the esterification of acyloxy carboxylicacids, and particularly to methods for esterifyingalphawacetoxypropionic acid, which can be made in quantity and at lowcost from lactic acid.

It is known that esters of acyloxy carboxylic acids can be made byacylating hydroxyesters such as methyl lactate or ethyl citrate. Forexample, methyl alpha-acetoxypropionate, which yields methyl acrylate onpyrolysis, can be made by acetylating methyl lactate with aceticanhydride or ketene (Smith et al., Ind. Eng. Chem. 34, 4'739 (April,1942)). Methyl alpha-acetoxypropionate has alsobeen made by treatingalphaacetoxypropionyl chloride with methanol. Previous methods formaking esters of acyloxy carboxylic acids have the disadvantage,however, of requiring such materials as acid anhydrides, acid chlorides,and ketene or ketene derivatives, which are more expensive than theparent carboxylic acids.

An object of this invention is to provide an improved method forconverting acyloxy carboxylic acids into their esters by directesterification.

A further object is to provide a continuous method for esterifyingacyloxy carboxylic acids, such as alpha-acetoxypropionic acid, withalcohols.

Other objects will appear from the following description:

I have found that acyloxy carboxylic acids can be esterified effectivelyby passing the acids and alcohol vapors countercurrently through a toweror column heated above the boiling point of the alcohol but below theboiling point of the desired ester. Moreover, I have found that thismethod of esterification can be carried out continuously. I have alsofound that the occurrence of side reactions leading to the formation ofundesired byproducts can be prevented or minimized by the operationswhich are a part of this invention.

The methods used in the present invention to esterify acyloxy carboxylicacids, which are particularly applicable to the esterification ofalphathe act of acetoxypropionic acid, are described below withreference to this acid.

Slightly different techniques were used in conducting the esterificationat atmospheric pressure the bottom of the packed tower.

and under vacuum. When the esterifications were carried out underreduced pressures, a mixture of alpha-acetoxypropionic acid, methanoland sulfuric acid was added dropwise into the top of a Pyrex glass tower(1" x 48") packed with /4" porcelain Berl saddles and electricallyheated. The temperature of the column was controlled and recordedautomatically. Methanol was passed into a heated vaporizing flask andthe vapor issuing from this flask was passed into The methanol vapor waspassed through the tower as long as alpha acetoxypropionic acid wasbeing passed into the column, and until the dry appearance of thepackingindicated that-all the acid had reacted. The vapors withdrawnfrom the top of the tower, which consisted of methanol, methylalpha-acetoxypropionate and other volatile produots, were passed intothe center of a steamjacketed. distillation column packed with smallBerl saddles. Methanol and water vapors which passed through thisstripping still were condensed. The 'products of higher boiling points,which were collected at the bottom of the distilling column, wereredistilled in a vacuum to determine the amounts or methyl lactate andmethyl alpha-acetoxypropionate obtained. Yields of methylalpha-acetoxypropionate as high as '72 to '75 percent were obtained atthe temperatures of 80 to 100 C.

' When alpha-acetoxypropionic acid was esterified with methanol vapor inthe packed tower under atmospheric pressure, the technique was slightlymodified. As before, methanol vapor and alpha-acetoxypropionic acid werepassed countercurrently through the tower, and the vapors withdrawn fromthe top of the tower were passed into the center of the steam-jacketeddistilling column. The methanol distilling from the top of the columnwas condensed and returned through a liquid seal to the heatedvaporizing flask. When the esteriflcation was carried out attemperatures below 108 C., the material collected at the bottom of thedistilling column con tained water and some methyl lactate and methylalpha-acetoxypropionate, but most or the esters passed downward throughthe esterlficatlon tower and were collected in a flask at the base. Thecontents of the flasks located at the bottom of both the distillationand esterification columns were distilled under reduced pressure todetermine the yields of methyl lactate and methylalpha-acetoxypropionate.

When the esterification was carried out in the packed tower underatmospheric pressure and at 2,402,129 3 e temperatures aboveapproximately 108 (3., the ica or alumina, may be used as packing toprom h -n l Vap r W s recycled and passed through mote theesteriflcation. Various types of esterithe tower until the appearance ofthe tower indification and distillation equipment may be used, catedthat all the alpha-acetoxypropionic acid including bubble cap columns.The mixed vapors had reacted and passed through the top of the 5withdrawn from the top of the tower may be tower into the distillingcolumn. The products distilled continuously or in batches to recover thecollected at the bottom of the distilling column desired ester andunchanged alcohol. Although were then distilled to separatethe'products. an esterification catalyst is preferably used, the Resultsobtained under the conditions described process may be operated in theabsence of such a above are set forth in Table I. V l catalyst.

Table L-Reactidn of alpha-acetoxypropionic acid with methanol vapor in apacked tower Methyl lactate Methyl alpha-acetoxypropionate gg?" Yield, gflgf Yield, per cent per cent per cent per cent v 0.5 0. 25 r 1. as 22 s0. a 0.10 1. 2 10, 72 .1. 0 0.20 3.8 11 7s 1.0 0.20 2.6 -17 72 p 1.00.20 2.1 0 72 1.0 0.20 1.3 8 1. 65

1.0 None 6.5 8 51 .1 0. 5 0. V V 1. 8 47- 34 1.0 None d 30 1 24 62 1. 00. 02 2. 0 21 25 55 1.0 0.05 0.5 a 7 50 1. 0 0. 05 7 0. 7 0 l0 60 1. 005 0. 0 e 11 54 1.0 0. 05 0.7 10 10 e0 1.0 0. 05 2.5 7 14 3s 71 V M10115ons may be made in practic- Having thus described my invention, I claim:ing this invention. For example, various pres- The process of preparingmethyl alpha-acetsures may be used in the esterification equipmentoxypropionate and methyl lactate simultaneously, and variousesterification catalysts, such as alkyl which comprises passingalpha-acetoxypropionic sulfates, hydrogen chloride, zinc chloride,phosacid and methanol vapor counter-currently phoric acid and arylsulfonic acids, may he used. through a reactor maintained at atemperature Other liquids, such as benzene, cyclohexane, and above theboiling point of methanol but below ether may be used to assist thedistillation of the the boiling point of the formed m thy phesterification products. The esterification tower acetoxypropionate, andrecovering the methyl or chamber may be packed with Berl saddles, lph tx pr p ona and the m hyl a Raschig rings, beads, crushed coke or withother packing materials. Active materials, such as sil- EDWARD M.FILACHIONE.

